linux-kernel - Re: [PATCH v1 31/31] serial: 8250_mxpcie: add RS485-2W auto-adjust sysfs control

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Message-ID: <CAHp75Vd4Fr9j3XF3Mxte8NDw_cE+_cyhWh=xs6YMQDTrmn=XnQ@mail.gmail.com>
Date: Mon, 1 Dec 2025 04:45:58 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Crescent Hsieh <crescentcy.hsieh@...a.com>
Cc: gregkh@...uxfoundation.org, jirislaby@...nel.org, 
	ilpo.jarvinen@...ux.intel.com, linux-kernel@...r.kernel.org, 
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v1 31/31] serial: 8250_mxpcie: add RS485-2W auto-adjust
 sysfs control

On Sun, Nov 30, 2025 at 12:46 PM Crescent Hsieh
<crescentcy.hsieh@...a.com> wrote:
>
> Moxa CP118E/CP138E/CP134EL/CP116E boards support a hardware "auto mode"
> in RS485-2W where the CPLD can automatically configure terminator and
> pull-state based on the selected baud rate and line condition. This mode
> is not meant to be kept enabled continuously — instead, it is triggered
> for a short period (about 2s) to let the hardware calibrate itself.
>
> This patch adds a write-only sysfs attribute that requests a one-shot
> hardware auto-adjust of terminator and pull-state. Writing a supported
> baud rate value (one of 9600, 19200, 38400, 57600, 115200, 230400,
> 460800, or 921600) into the attribute programs the CPLD baud code and
> runs a temporary AUTO mode cycle (about 2s) on RS485-2W ports of the
> supported boards. Invalid interfaces or devices are rejected.

I'm not going to review this, the patch series is already quite big. I
suggest you to start from the small things in a different series E.g.,
the first series is just converting MOXA from custom to 8250-based
(assuming all features are kept working while ABI is being broken,
which has to be explained in the commit message(s) / cover letter of
that series), the second one is about splitting 8250_pci to the other
Moxa case. When this is done, we may go forward with the additional
features.

-- 
With Best Regards,
Andy Shevchenko